The present invention relates to the field of telecommunications, and more specifically, to the field of power control in wireless telephones.
Conventional portable wireless telephones are powered by rechargeable batteries. The operational life of the wireless telephone between battery charges is directly dependent on the charge life of the battery. In addition, the charge life of a battery is related to the battery size, which is a major factor in determining the weight of the phone since batteries are generally relatively heavy compared to the remaining elements of the phone. Thus, the battery is a critical component of the phone and is a major factor in determining the phone's physical and operational characteristics, i.e. size, weight, and operational life span.
In an effort to make portable wireless telephones smaller, more portable, and of greater operational life between battery charges, the wireless telephone industry is continually searching for ways to extend the charge of the battery. The power consumption of the phone is important since a phone that uses less power will operate longer per battery charge. Furthermore, a phone that uses less power can be powered by a smaller, lighter battery and still retain an acceptable operational life span between battery charges. As a result, the phone unit is less massive, more portable, and generally more convenient to use.
The conventional method followed by a mobile station (wireless telephone) when attempting to access a base station is to continuously scan available carrier spectrums in search of acceptable signals from a base station. According to the conventional method, if the mobile station fails to find and begin communication with a base station after searching through the available carrier spectrums, the search process continues rotating through the available carrier spectrums searching for acceptable base station signals until a base station is accessed, the mobile station is turned off by a user, or the battery becomes depleted of usable energy. Unfortunately, the conventional mobile station has no other way of knowing if a base station is accessible or when one will become accessible. Therefore, the mobile station wastes power and reduces the charge life of the battery as it continuously searches for a base station when the mobile station is in an area not covered by wireless service or where service is otherwise unavailable, such as a result of carrier selection programming, maximum caller volume, etc.
Multi-mode mobile stations are capable of operating in two or more different modes for use in two or more different types of communication systems, such as conventional analog FM (frequency modulation), digital CDMA (code division multiple access), digital TDMA (time division multiple access), and others. Among the various types of radios and communication devices, one particular type of multi-mode communication device is a dual-mode CDMA/FM radio telephone capable of operating in both analog FM systems and digital CDMA systems. This type of mobile station is able to search for base station signals in CDMA and FM carrier spectrums. Any given cellular area throughout the United States is currently serviced by up to two competing providers of cellular airtime communication services. The two service providers in any given geographic area are commonly referred to as "A" and "B" carriers and are assigned different groups of frequencies or frequency sets. It is, of course, up to each service provider to decide which types of communication modes to support, as well as how many channels and resources to devote to each mode. For areas in which each service provider supports both CDMA and FM communication modes, a typical dual-mode CDMA/FM cellular mobile station continually rotates through the CDMA "A", FM "A", CDMA "B", and FM "B" carrier spectrums searching for base station signals. The order in which these systems are searched is typically determined by mobile station programming.
According to conventional dual-mode CDMA/FM searching methods, besides continuously rotating through all supported carrier spectrums, the mobile station repeatedly searches through all potential base station locations associated with a particular carrier spectrum until either an acceptable base station signal is found or a maximum search time limit expires for that type of carrier spectrum. When in a CDMA searching mode, the conventional dual-mode CDMA/FM mobile station continuously searches for acceptable base station signals by searching for a valid CDMA base station pilot channel. Pilot channel signals are transmitted by all CDMA base stations using the same pseudo-random number (PN) code. However, pilot channel signals are transmitted with different PN code timing offsets to allow the base stations to be distinguished by the mobile station. The mobile station searches repeatedly through all PN code timing locations (timing hypotheses) when attempting to acquire a CDMA base station pilot channel. Unless an acceptable base station pilot signal is detected before a maximum search time limit expires, the mobile station begins searching instead for acceptable base station signals in the next carrier spectrum, such as, for example, the FM "A" carrier spectrum. When searching in, for instance, the FM "A" carrier spectrum, the typical dual-mode CDMA/FM cellular mobile station repeatedly searches through all available frequency channels (frequency locations) in that carrier spectrum (i.e., FM "A") in an attempt to find an acceptable analog base station signal. Unless an acceptable base station signal is detected before a maximum search time limit expires, the mobile station begins searching instead for acceptable base station signals in the next carrier spectrum, such as, for example, the CDMA "B" carrier spectrum. Consequently, the conventional searching methods are very time-consuming and wasteful of mobile station battery power.
There is, therefore, a need in the industry for a system which addresses these and other related, and unrelated, problems.